Many different types of pointing devices have been developed for inputting commands into a machine. For example, hand-manipulated pointing devices, such as computer mice, joysticks, trackballs, touchpads, and keyboards, commonly are used to input instructions into a computer by manipulating the pointing device. Such pointing devices allow a user to control movement of a cursor (i.e., a virtual pointer) across a computer screen, select or move an icon or other virtual object displayed on the computer screen, and open and close menu items corresponding to different input commands.
Pointing devices have been developed for large electronic devices, such as desktop computers, which are intended to remain stationary, and for small portable electronic devices, such as cellular telephones and mobile computer systems. Pointing devices for large electronic devices typically have fewer and more flexible design constraints than pointing devices for portable electronic devices because of the greater space and power resources that are available. In general, a pointing device for use in portable electronic devices should allow a user to move a cursor quickly and accurately, operate in an intuitive fashion, and operate within limited workspace and power constraints.
Displacement type pointing devices have been developed to meet the constraints inherent in portable electronic devices. These types of pointing devices include a displaceable member (e.g., a puck, button, or other movable body) that moves in a defined field of motion upon application of force by, for example, a user's finger. In a typical displacement-type pointing device, the displaceable member moves in two dimensions in response to lateral forces that are directed in a plane. Resistor circuits, capacitive sensors, and magnetic (Hall-effect) sensors have been used to determine the displacement of the displaceable member within the field of motion. The determined displacement of the displaceable member is mapped to two-dimensional motion of a cursor on a display. A restoring mechanism (e.g., a set of springs) typically returns the displaceable member to a central location within the field of motion after the user releases the displaceable member. The position mapping system typically fixes the position of the cursor on the display when the displaceable member is in the central location of the field of motion.
The field of motion of the displaceable member typically is very small. As a result, displacement type pointing devices typically operate in either a relative device-cursor mapping mode or a velocity mapping (or joystick) mode. In a relative device-cursor mapping mode, the position of the displaceable member and the position of the cursor on the display can be offset with a variable mapping. In a velocity mapping mode, the displacement of the displaceable member is mapped to the velocity of the cursor on the display. The field of motion of the displaceable member typically is too small to provide an absolute device-cursor mapping mode in which there is a one-to-one correspondence between the position of the displaceable member and the position of the cursor on the screen.
What are needed are displacement type pointing device and methods that are capable of sensing movement of the displaceable member with high accuracy and provide an absolute position mapping mode of input in which there is a one-to-one correspondence between the positions of the displaceable member and the positions of a cursor on a display.